Human adipocyte lipid-binding protein (aP2) belongs to a family of intracellular lipid-binding proteins involved in the transport and storage of lipids (Banzszak et al., (1994) Adv. Protein Chem. 45, 89-151). The aP2 protein is involved in lipolysis and lipogenesis and has been indicated in diseases of lipid and energy metabolism such as diabetes, atherosclerosis, and metabolic syndromes. aP2 has also been indicated in the integration of metabolic and inflammatory response systems. (Ozcan et al., (2006) Science 313(5790):1137-40; Makowski et al., (2005) J Biol Chem. 280(13):12888-95; and Erbay et al., (2009) Nat Med. 15(12):1383-91). More recently, aP2 has been shown to be differentially expressed in certain soft tissue tumors such as certain liposarcomas (Kashima et al., (2013) Virchows Arch. 462, 465-472).
aP2 is highly expressed in adipocytes and regulated by peroxisome-proliferator-activated receptor-γ (PPARγ) agonists, insulin, and fatty acids (Hertzel et al., (2000) Trends Endocrinol. Metab. 11, 175-180; Hunt et al., (1986) PNAS USA 83, 3786-3790; Melki et al., (1993) J. Lipid Res. 34, 1527-1534; Distel et al., (1992) J. Biol. Chem. 267, 5937-5941). Studies in aP2 deficient mice (aP2−/−) indicate protection against the development of insulin resistance associated with genetic or diet-induced obesity and improved lipid profile in adipose tissue with increased levels of C16:1n7-palmitoleate, reduced hepatosteatosis, and improved control of hepatic glucose production and peripheral glucose disposal (Hotamisligil et al., (1996) Science 274, 1377-1379; Uysal et al., (2000) Endocrinol. 141, 3388-3396; Cao et al., (2008) Cell 134, 933-944).
In addition, genetic deficiency or pharmacological blockade of aP2 reduces both early and advanced atherosclerotic lesions in the apolipoprotein E-deficient (ApoE−/−) mouse model (Furuhashi et al., (2007) Nature, June 21; 447(7147):959-65; Makowski et al., (2001) Nature Med. 7, 699-705; Layne et al., (2001) FASEB 15, 2733-2735; Boord et al., (2002) Arteriosclerosis, Thrombosis, and Vas. Bio. 22, 1686-1691). Furthermore, aP2-deficiency leads to a marked protection against early and advanced atherosclerosis in apolipoprotein E-deficient (ApoE−/−) mice (Makowski et al., (2001) Nature Med. 7, 699-705; Fu et al., (2000) J. Lipid Res. 41, 2017-2023). Hence, aP2 plays a critical role in many aspects of development of metabolic disease in preclinical models.
In the past two decades, the biological functions of FABPs in general and aP2 in particular have primarily been attributed to their action as intracellular proteins. Since the abundance of aP2 protein in the adipocytes is extremely high, accounting for up to few percent of the total cellular protein (Cao et al., (2013) Cell Metab. 17(5):768-78), therapeutically targeting aP2 with traditional approaches has been challenging, and the promising success obtained in preclinical models (Furuhashi et al., (2007) Nature 447, 959-965; Won et al., (2014) Nature Mat. 13, 1157-1164; Cai et al., (2013) Acta Pharm. Sinica 34, 1397-1402; Hoo et al., (2013) J. of Hepat. 58, 358-364) has been slow to progress toward clinical translation.
In addition to its presence in the cytoplasm, it has recently been shown that aP2 is actively secreted from adipose tissue through a non-classical regulated pathway (Cao et al., (2013) Cell Metab. 17(5), 768-778; Ertunc et al., (2015) J. Lipid Res. 56, 423-424). The secreted form of aP2 acts as a novel adipokine and regulates hepatic glucose production and systemic glucose homeostasis in mice in response to fasting and fasting-related signals. Serum aP2 levels are significantly elevated in obese mice, and blocking circulating aP2 improves glucose homeostasis in mice with diet-induced obesity (Cao et al., (2013) Cell Metab. 17(5):768-78). Importantly, the same patterns are also observed in human populations where secreted aP2 levels are increased in obesity and strongly correlate with metabolic and cardiovascular diseases in multiple independent human studies (Xu et al., (2006) Clin. Chem. 53, 405-413; Yoo et al., (2011) J. Clin. Endocrin. & Metab. 96, E488-492; von Eynatten et al., (2012) Arteriosclerosis, Thrombosis, and Vas. Bio. 32, 2327-2335; Suh et al., (2014) Scandinavian J. Gastro. 49, 979-985; Furuhashi et al., (2011) PloS One 6, e27356; Ishimura et al., (2013) PloS One 8, e81318; Karakas et al., (2009) Metabolism: Clinical and Experimental 58, 1002-1007; Kaess et al., (2012) J. Endocrin. & Metab. 97, E1943-1947; Cabre et al., (2007) Atherosclerosis 195, e150-158). Finally, humans carrying a haploinsufficiency allele which results in reduced aP2 expression are protected against diabetes and cardiovascular disease (Tuncman et al., (2006) PNAS USA 103, 6970-6975; Saksi et al., (2014) Circulation, Cardiovascular Genetics 7, 588-598).
Cao et al. used a rabbit anti-mouse aP2 polyclonal antibody to show a reduction in plasma aP2 levels in obese antibody-treated mice, which occurred without any alteration in aP2 protein levels in the adipose tissue (Cao et al., (2013) Cell Metab. 17(5): 768-778; PCT Publication WO 2010/102171). Administration of the antibody in obese mice did not alter the body weight, but did cause a significant decrease in fasting blood glucose levels within two weeks of treatment compared to controls treated with a pre-immune IgG. In a glucose tolerance test, mice receiving the aP2 polyclonal antibody exhibited significantly improved glucose disposal curves compared to control animals.
Miao et al. reported the use of a high affinity mouse anti-human aP2 monoclonal antibody (identified as mAb 2E4) to achieve improved high-fat diet (HFD) induced inflammation in antibody treated mice receiving a high-fat diet (Miao et al., (2015) Molecular and Cellular Endocrinology 403, 1-9). Treatment with the high affinity mAb 2E4, however, resulted in drastically increased body weights compared with control animals, and no notable change was observed in basal glucose levels after six weeks of treatment. Furthermore, mAb 2E4 treatment failed to affect HFD-induced insulin tolerance.
It is an object of the invention to identify new compounds, methods, and compositions for the treatment of metabolic disorders.
It is in particular an object of the invention to identify new compounds, methods, and compositions for the reduction of fasting blood glucose levels, the improvement of systemic glucose metabolism, the improvement of glucose tolerance, the increase in systemic insulin sensitivity, the reduction in fat mass, the reduction in fat cell lipolysis, the reduction in hepatic glucose production, the reduction in hyperinsulinemia, and/or the reduction in liver steatosis.
It is also an object of the invention to identify new compounds, methods, and compositions for the treatment of diabetes, obesity, and dyslipidemia.
It is further object of the invention to identify new compounds, methods, and compositions for the treatment of inflammatory induced disorders, for example atherosclerosis.
It is another object of the invention to identify new compounds, methods, and compositions for the treatment of a tumor, cancer, or other neoplasm.